1. Field of the Invention
The present invention relates to the field of rotary stencil printer, and more particularly, to a device for mounting a leading end of a print sheet of a rotary stencil printer having a printing drum for carrying a stencil sheet therearound and a back press means having a surface for supporting the print sheet such that the print sheet is transferred through between the printing drum and the back press means with the leading end thereof being mounted to the back press means by the print sheet leading end mounting device so as to be applied with a stencil printing thereon.
2. Description of the Prior Art
As a countermeasure for avoiding the back contamination of printed sheets which occurs when the printed sheets produced by the stencil printing are immediately laid one over the other, it has been proposed by Japanese Patent Application 4-163590 (Laid-open Publication 5-330244) filed on 29 May 1992 by the same applicant as the present application by claiming a domestic priority based upon Japanese Patent Application 3-162218 filed on 6 Jun. 1991, to decrease the thickness of an ink layer provided on the surface of a print sheet by the stencil printing to be the necessary minimum required for providing a clear indication of a printed image, by supplying ink to a perforated stencil sheet on one surface thereof in the form of an ink layer, with the other surface of the stencil sheet having been pressed against a surface for printing, then applying a pressure to the ink layer by a pressing means such that the ink of the ink layer is transferred from said one surface to said other surface of the stencil sheet through perforations of the stencil sheet to be attached on the surface for printing, and then to remove the surface for printing from said other surface of the stencil sheet at a portion where any substantial flow of the ink of the ink layer relative to the stencil sheet is held by the pressing means which has applied the pressing force to the ink layer under the condition that said other surface of the stencil sheet is in a tight contact with the surface for printing, and further to provide, in carrying out the stencil printing according to the above-mentioned principle by a rotary stencil printer, a device for selectively mounting the leading end of a print sheet to a back press means which supports the print sheet against a printing drum carrying a stencil sheet such that the print sheet provided with an ink image thereon by the pressing contact with the printing drum carrying the stencil sheet under the support of the back press means is, after the application of the stencil printing, forcibly removed from the printing drum as firmly held on the back press means, wherein said device for selectively mounting the leading end of a print sheet to the back press means is a claw-like clamp member adapted to selectively clamp the leading end of a print sheet to the print sheet supporting surface of the back press means.
When the print sheet leading end mounting device of the above-mentioned construction operates to conduct the leading end of a print sheet through a nip region where the printing drum and the back press means are pressed against one another, if the clamp member is protrudent above the print sheet supporting surface of the back press means, smooth operation of the rotary stencil printer is obstructed. Therefore, it is desired that, when such a print sheet leading end mounting device is in the operating condition, the claw-like clamp member is sunk below the contour of the print sheet supporting surface of the back press means. However, the condition that the claw-like clamp member is sunk below the contour of the print sheet supporting surface of the back press member implies that the leading end of a print sheet clamped by the clamp member is bent into the inside of the back press means relative to a principal portion of the print sheet following the leading end as supported on the print sheet supporting surface of the back press means.
When the leading end of a print sheet mounted to the back press means by the claw-like clamp member has been bent against the following principal portion thereof so as to sink below the contour of the print sheet supporting surface of the back press means, it occurs that, when the printing process proceeds so far that the clamping of the leading end by the clamp member is released for the print sheet to be removed from the back press means, starting from the leading end, by a print sheet removal claw member being engaged under the leading end of the print sheet, the leading end of the print sheet bent below the contour of the print sheet supporting surface of the back press means is not engaged by the tip of the print sheet removal claw member, endangering a regular transfer of the print sheet toward a print sheet disposal means.